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Catabolism of L-Ascorbic Acid in Guinea Pigs¹

Department of Biochemistry and Nutrition, The University of Texas Medical Branch, Galveston, Texas

As an extension of earlier work on the catabolism of ascorbic acid in guinea pigs, investigations on the initial phase following administration of ascorbic-1-C¹⁴ acid were made. Catabolism during this stage has the characteristics of first-order processes, was kinetically independent of the following slower phase, and could be "saturated" by injection of high levels of ascorbic acid. The rapid initial reaction did not appear to depend upon renal action and was unchanged by intrahepatic injection of ascorbic-1-C¹⁴ acid.

Massive doses of labeled ascorbic acid in normal guinea pigs were catabolized similar to more physiological doses, except for higher levels of urinary excretion of radioactivity and conversion of a lower fraction of the dose to respiratory C¹⁴O₂ during the initial phase. Contraction of the body pool of ascorbic acid exerted no direct effect on the catabolism of ascorbic acid. Such diminution in catabolism as was discovered after prolonged feeding of a scorbutigenic diet was presumably referable to general metabolic impairment, rather than to a specific response designed to protect, or coincidentally protecting, against the consequences of the scorbutigenic regimen.

As anticipated from the kinetics of the rate-limiting processes, newly-administered ascorbic acid did not cause sparing of that already incorporated into the tissues.

Manuscript received 13 October 1961.